The Story of Henry Molaison
One fall morning in Hartford, Connecticut, in 1953, a 27-year-old man named Henry Molaison sat down for a medical procedure. Doctors were trying to cure him of severe epilepsy. They theorized that the source of his condition lay in the area of his brain known as the hippocampus.
Their solution? Hammer a spike into his brain and cut the whole hippocampus out, along with his amygdala.
The procedure – a temporal lobotomy – was, in one sense, successful. Molaison’s epilepsy was cured. But this story is more famous for the side effect that came as a result.
Henry Molaison was left unable to form any new memories ever again. Every day he woke up, the last thing he could remember was the day before his lobotomy – September 1st, 1953. This was true for the rest of his life – right up to his death in 2008.
Molaison’s famous case proved what some scientists had already hypothesized – that new memories are created in the hippocampus, and that they stay there for a while before being encoded as long-term memories in the cerebral cortex.
This finding is crucial in understanding how we make the leap from short-term retention to long-term memory – the essence of how we truly learn.
The Memory Seahorse
The crucial part of the brain to forming new memories – the part that the unfortunate Henry Molaison lost – is the hippocampus. The word comes from Latin: ‘hippocampus’ is the Latin word for ‘seahorse,’ and this part of the brain got its name because it looks like one.
This little seahorse, buried deep in the very center of your brain, decides which bits of brain activity – or neural pathways – get stored as memories. More specifically, these are ‘explicit memories.’ Explicit memories cover both conscious memories of events, known as episodic memories, and of facts and abstract concepts, known as semantic memories.
The difference between episodic and semantic memories will be important, so remember: episodic memory is remembering events (think ‘episodes’), and semantic memory is knowing facts.
Both of these kinds of memory are initially stored as short-term memories in the hippocampus. Over time, some of those short-term memories will be converted into long-term memories that are stored in the neocortex, in the outer layer of the brain.
Short-Term First, Long-Term Second
We’ve thrown around a few big words, but don’t worry – the important thing for our purposes is that newly learned information doesn’t go straight into your long-term memory. Instead it sits in the hippocampus for a while, before some of it is converted into long-term memories, which are stored in the neocortex, and are altogether different than short-term ones.
An imperfect analogy that might be helpful is between the brain and a computer – the hippocampus is a little like your RAM temporarily storing an input, and your neocortex is the hard drive, which will permanently save some of that information if needed.
Neuroscientists will probably take issue with this analogy, so please bear in mind that it is a rough one! Kinnu’s pathways on AI and human cognition both explain why the analogy between brains and computers can be misleading.
Anyway, what we’ve been discussing begs the question: what leads some information to make it into long-term memory, while most never does? In truth, a lot remains unknown about this, but there are 2 factors that we can say with some confidence are influential on this process.
These are repetition and reward.
The Role of Repetition
The first factor that influences whether a memory is transmitted from short-term to long-term memory is repetition.
This is because of the difference between episodic and semantic memory that we discussed earlier – memory of events and memory of facts.
The hippocampus stores short-term memories as episodic memory. This is true even for facts – if you learned something this morning, and try to remember it in the afternoon, the chances are that you will be remembering the moment you learned it, rather than remembering the fact itself.
But, in the long term, it’s the semantic memory that sticks – you know that the Earth is a sphere, but can you remember the elementary school lesson where you were taught it? It’s possible – but for most of us, we just have this stored as a semantic fact.
The way this episodic recollection gets translated into semantic knowledge is through the hippocampus recognizing the same pathways being repeatedly activated.
The hippocampus distills long-term semantic memories from episodic ones, when it recognizes the same neural pathways being repeatedly activated.
Let’s return to the example of learning the shape of the Earth. As a 6-year-old you probably didn’t absorb this information straight off the bat. There were probably more important things to focus on, like Lego Star Wars or pulling your sister’s hair.
But you will have been exposed to this piece of information repeatedly over time. Your teacher would tell you, then you’d do some homework. You’d see images of the Earth here and there, and perhaps get taken to a planetarium.
Internally, your hippocampus would have recognized the same thought occurring several different times: ‘the world = a sphere’. Once this pathway has been activated enough times, the hippocampus will recognize it as a semantic fact, and store it in the neocortex. Now the memory has shifted from short-term episodic information – ‘my teacher said the earth is a sphere’ – to long-term semantic memory – ‘I know that the Earth is a sphere.’
Using Your Hippocampus to Learn
So this little seahorse-y brain structure is the key to committing stuff to your long-term memory. It’s able to identify repeated patterns in the information it receives, and will eventually encode them as long-term memory.
This has several implications for how best to learn new information.
Learning needs to be an exercise in repeating those neural pathways – basically by absorbing the information on several occasions, at spaced intervals. This technique is called ‘spaced repetition.’
In practice, this might mean sitting a lesson one day, and checking your notes that evening. Then, taking another look at your notes, and maybe some similar lectures on YouTube, 2 days later. Finally you’d want to revisit the information a week later.
Alternatively, you might want to use a spaced repetition app like Kinnu. But if you’re here, you already know that!
Over time, the hippocampus will recognize the familiar pathway, and will cease to view it as a one-off episode, and start to encode it into the neocortex.
A wealth of recent research has suggested that this encoding happens much more during sleep. This is because the hippocampus encodes stuff for long-term storage much more effectively if it doesn’t have to identify new pathways from lots of new brain processes at the same time.
The Reward System and Motivation
We’ve now covered how repetition encourages our brain to encode information into our long-term memory. But the ability to memorize new information isn’t the only aspect of learning. Another huge part of learning is motivation.
Motivation is the reason you want to learn something in the first place. Understanding the neuroscience behind it is highly important to understanding how to learn successfully.
The key area of the brain that deals with motivation is called the reward system. This system is made up of several parts, but, for our purposes, we will be considering the prefrontal cortex and the amygdala.
In a broad sense, these 2 parts of the reward system can encourage the hippocampus to encode information using 2 motivation tactics that we all understand – the carrot (the prefrontal cortex), and the stick (the amygdala).
The amygdala is a tiny acorn-like bulb, sitting right next to the seahorse-shaped hippocampus. This acorn has been behind every feeling of stress, fear and anxiety you’ve ever felt.
The amygdala processes intense emotional stimuli. Memories that have been associated with emotional stimuli in the amygdala will be encoded more quickly into the long term by the hippocampus.
This is because the amygdala triggers the release of stress hormones – raising your heart rate and making you sweat – for neural pathways that it recognizes as potentially dangerous.
This has an obvious function – your brain wants to remember the stuff that was most harmful in the past, encoding it to long-term memory so that it knows how to avoid harm in the future.
Your hippocampus will encode memories more quickly when they are accompanied by this stress response from your amygdala. Pathways that have been accompanied by this heightened activity from stress hormones will be fast-streamed into the neocortex.
If You Can Dodge a Wrench, You Can Dodge a Ball
To think about how the amygdala helps encode memory, let’s look at a character in the classic comedy Dodgeball called Patches O’Houlihan.
Patches is a dodgeball coach whose training technique involves carrying a big sack of monkey wrenches with him at all times. At random intervals, when a team member isn’t expecting it, he throws one at their head.
In the coach’s words, “if you can dodge a wrench, you can dodge a ball.” The aim is to give them such intense fear of being hit by his wrench that their reactions to dodging flying objects – including, of course, balls – become lightning-fast.
This more or less illustrates the role of the amygdala in speeding up the hippocampus’s encoding of memories. The amygdala has identified an extremely painful experience, and the hippocampus has fast-streamed the knowledge – ‘flying objects will really hurt you’ – straight to the neocortex as a result.
All it takes is a powerful emotional association with an event and the hippocampus will ensure you don’t forget it in a hurry. “If you can dodge a wrench, you can dodge a ball.”
So, one aspect of your brain’s motivation to learn is ‘the stick’ – the amygdala speeding the process up through the release of stress hormones. This means that you will find yourself learning information that has an emotional significance to you much more quickly.
The second way that the reward system influences your brain’s motivation is through the carrot – the prefrontal cortex and dopamine pathways.
The prefrontal cortex is the part of your brain that deals with high-level goals and delayed gratification. It’s best thought of as the responsible, grown-up part of your brain.
While other parts of the brain might be saying ‘maybe I do need to watch “Top Ten Unexpected Deaths in Game of Thrones”,’ the prefrontal cortex is the part that says, ‘you’ve already spent the past 45 minutes on YouTube!’
Long-Term Goals and Dopamine
The prefrontal cortex works by storing long-term goals. Some of these are learned – ‘I want to buy a house one day’, others are instinctive – ‘I want my children to be safe.’
In either case, the prefrontal cortex uses these goals to influence the memory encoding process we discussed earlier. It does this through the brain’s dopamine pathways.
You may know dopamine as the ‘happy hormone.’ This is broadly accurate. Dopamine is a neurotransmitter – a chemical that sends messages from one part of the brain to the other. In the case of dopamine, this is a reward message – the brain will use dopamine to communicate the message ‘this is good, we need to keep doing this!’
How the Prefrontal Cortex Helps the Memory
The prefrontal cortex sends a reward message through the dopamine pathway when it recognizes activity in the hippocampus that aligns with its long-term goals.
Essentially, it spots neural pathways that will help contribute to the long-term goals that it values. It will then send a little hit of dopamine to the hippocampus, that will both encourage it to encode that pathway as a memory and trigger a feeling of contentment.
Let’s say your goal is to become a basketball player. You have an image in your head of yourself hitting the winning free throw in the NBA play-offs.
You practice for hours and hours to hit free throws consistently. Every time you hit that free throw, the image in your hippocampus matches up to that stored image on your prefrontal cortex. A little dopamine is released and the memory of how you threw the ball that time is recognized as more valuable by your hippocampus, which will encode it for long-term storage.